Re: inductor sizing


<tech@xxxxxxxxxxxxxxxxx> wrote in message news:29c44219-0854-4208-8c9b-495c61517ac6@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
I am absolutely in awe to the welth of information found here. If I
may? I am working on a similar power supply, with similar requirements
as the origional poster save the 60hz final output. The supply I am
working on will be directly controlling the current with little focus
on the actual voltage.

The Basics, 208Vac 3phase or 220Vac single phase input rectified and
filtered.
I would like to use a bank of mosfets at a switching frequency around
200-250 Khz
Or another possibility would be a large IGBT at around 10-12 Khz.
Drive and controll considerations asside, I am looking for 2% or less
of THD if possible
output current will average 20-35A with a sustained 50A possible. The
output voltage will be anywhere from 95V to as much as 160V DC. The
full voltage of the rectified mains will be on the output untill the
sustained arc is started and at which point the current regulation
will be put to work. The voltage will vary and that is expected but
the current must stay stable. I have a pretty good design on the
controlls and feedback, But...
My question is weather to use a bank of mosfets with there own LC
network each, such as 5 or 6 in parallel with all outputs tied
together, or1 bank of mosfets\IGBT and a single filter?

Much Thanks
Cory

Hi Cory, let me take a shot at restating your requirements. AC to DC converter. Input, 220Vac or 208V-3phase, 50 or 60 Hz with THD of the input current <2% . So you need a PFC stage that will output about 550Vdc at 5.0Kws. The PFC is followed by a Dc/Dc converter that will output 160Vdc and current limit at 20A to 50A, externally control. The 550Vdc to 160Vdc converter sounds like a phase shifted bridge, maybe 2 bridges, driven 180d out of phase, driving into two transformers with output rectifiers driving one or two output inductors summing into a array of filter capacitors. The output inductors are operating at a high DC current and lower AC current, much different from our previous design.
As far as parallel or single MOSFETS, a lot of trade off must be done before a final topology can be decided. Take a look at two or three phase shifted bridges, operating at ZVS to reduce the output stress on the LC filter.
Hope this helps,
Harry

.

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